Is it OK to remove inlet NRVs from thermostatic bar mixer shower valve in gravity fed system?

14 Jan 2018
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United Kingdom
I have just changed my very old mixer for a Triton Pirlo thermostatic bar mixer shower (from Screwfix) but the flow/pressure is now barely acceptable. I've tried different shower heads including ones designed for low pressure systems with little improvement. The shower and hot water cylinder are on the 1st floor, the cold water tank in the loft about 1-2 m above, and theshower hose to the shower head is wide bore (12 mm). I see that the Triton has NRVs at the inlet on both the hot and cold side and wondered if removing them is safe to hopefully increase the shower flow/pressure? A shower fitted to a mixer tap on the bathroom also on the 1st floor is working fine with good flow and pressure, which makes me think it is something to do with the Triton.
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No idea what the minimum pressure requirements are for the Pirlo valve ,but you are unlikely to have more than 0.2 bar with your set up. Some bar mixers work better than others with low pressure / gravity set ups. Removing the NRV' s won't do any real harm ,if the cold is from the loft tank ,but the difference in flow will not be substantially more.
I suggest you try removing the NRVs. That will definitely increase the flow rate through the shower valve, hopefully by enough to satisfy your needs.
Be aware though, that some shower valves may allow hot to cross into the cold pipework (and vice-versa) when drawing at high rates elsewhere, such as the bath taps. Watch out for signs that the hot side (usually the left) goes cold or the cold side gets warmer as you fill the bath.
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Thanks for the advice. I will remove the two NRVs and post the result.

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